Method of mixing at least two gases

ABSTRACT

A method of mixing at least two gases is provided. This method includes providing a mixture composition control, including a predetermined composition input and a composition trim input. Providing N gas flow meters, including a N gas flows, and N desired gas flow rates determined by the mixture composition control, wherein N is 3 or more. Mixing the N gas flows, thereby producing a mixed gas flow at the predetermined composition and at a line pressure. Configuring the N flow meters to adjust the N gas flows to maintain the line pressure at a predetermined value, while maintaining the predetermined composition. And adjusting the composition trim input to vary the composition of the mixed gas, without modifying the predetermined composition input.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 119(a) and (b) and to U.S. Provisional Patent Application No. 62/462,441,filed Feb. 23, 2017, the entire contents of which are incorporatedherein by reference.

BACKGROUND

Gas blending is the process of mixing gases for a specific purpose wherethe composition of the resulting mixture is specified and controlled. Awide range of applications include scientific and industrial processes,food processing and/or packaging, and breathing gases. Examples includeshielding gases for welding, modified atmosphere packing in the foodindustry, breathing gas mixtures for diving, medical gas mixtures,chemical production processes, and calibration gases. Reliable,repeatable, accurate, and precise mixing of the various constituentgases is very important.

SUMMARY

A method of mixing two gases is provided. The method includes providinga mixture composition control including a mixed gas flow at apredetermined composition. Providing a first gas flow meter, including afirst gas flow, and a first desired gas flow rate determined by themixture composition control. Providing a second flow meter, including asecond gas flow, and a second desired gas flow rate determined by themixture composition control. Mixing the first gas flow and the secondgas flow, thereby producing the mixed gas flow at the predeterminedcomposition and at a line pressure. And configuring the first flow meterand the second flow meter to adjust the first gas flow and second gasflow to maintain the line pressure at a predetermined value, whilemaintaining the predetermined composition.

Another method of mixing at least two gases is provided. This methodincludes providing a mixture composition control including a mixed gasflow at a predetermined composition. Providing N gas flow meter,including N gas flows, and N desired gas flow rate determined by themixture composition control, wherein N is 3 or more. Mixing the N gasflows, thereby producing the mixed gas flow at the predeterminedcomposition and at a line pressure. And configuring the N flow meters toadjust the N gas flows to maintain the line pressure at a predeterminedvalue, while maintaining the predetermined composition.

This method includes providing a mixture composition control, includinga predetermined composition input and a composition trim input.Providing a first gas flow meter, including a first gas flow, and afirst desired gas flow rate determined by the mixture compositioncontrol. Providing a second flow meter, including a second gas flow, anda second desired gas flow rate determined by the mixture compositioncontrol. Mixing the first gas flow and the second gas flow, therebyproducing a mixed gas with a predetermined composition. And adjustingthe composition trim input to vary the composition of the mixed gas,without modifying the predetermined composition input.

Another method of mixing at least two gases is provided. This methodincludes providing a mixture composition control, including apredetermined composition input and a composition trim input. ProvidingN gas flow meters, including N gas flows, and N desired gas flow ratesdetermined by the mixture composition control. Mixing the N gas flows,thereby producing a mixed gas with a predetermined composition. Andadjusting the composition trim input to vary the composition of themixed gas, without modifying the predetermined composition input.

Another method of mixing two gases is provided. This method includesproviding a mixture composition control, including a predeterminedcomposition input and a composition trim input. Providing a first gasflow meter, including a first gas flow, and a first desired gas flowrate determined by the mixture composition control. Providing a secondflow meter, including a second gas flow, and a second desired gas flowrate determined by the mixture composition control. Mixing the first gasflow and the second gas flow, thereby producing a mixed gas flow at thepredetermined composition and at a line pressure. Configuring the firstflow meter and the second flow meter to adjust the first gas flow andsecond gas flow to maintain the line pressure at a predetermined value,while maintaining the predetermined composition. And adjusting thecomposition trim input to vary the composition of the mixed gas, withoutmodifying the predetermined composition input.

Another method of mixing at least two gases is provided. This methodincludes providing a mixture composition control, including apredetermined composition input and a composition trim input. ProvidingN gas flow meters, including a N gas flows, and N desired gas flow ratesdetermined by the mixture composition control, wherein N is 3 or more.Mixing the N gas flows, thereby producing a mixed gas flow at thepredetermined composition and at a line pressure. Configuring the N flowmeters to adjust the N gas flows to maintain the line pressure at apredetermined value, while maintaining the predetermined composition.And adjusting the composition trim input to vary the composition of themixed gas, without modifying the predetermined composition input.

BRIEF DESCRIPTION OF THE FIGURES

For a further understanding of the nature and objects for the presentinvention, reference should be made to the following detaileddescription, taken in conjunction with the accompanying drawings, inwhich like elements are given the same or analogous reference numbersand wherein:

FIG. 1 is a schematic representation the method for mixing two gases,accordance with one embodiment of the present invention.

FIG. 2 is a schematic representation the method for mixing N gases,accordance with one embodiment of the present invention.

FIG. 3 is a schematic representation the method for determining thecalculated theoretical percentage for two gases, in accordance with oneembodiment of the present invention.

FIG. 4 is a schematic representation the calculated theoreticalpercentage calculator for N gases, in accordance with one embodiment ofthe present invention.

FIG. 5 is a representative representation of the flow mixers, inaccordance with one embodiment of the present invention.

ELEMENT NUMBERS

-   101=Signal from First Flow Meter to CTP Calculator-   102=Signal from Second Flow Meter to CTP Calculator-   103=First Flow Meter-   104=First Gas (Inlet)-   105=Second Flow Meter-   106=Second Gas (Inlet)-   107=Flow Sensor (internal to Flow Meters 102, 105, 113, and 116)-   108=Combined Gas Flow-   109=Alarm-   110=Data Logging System-   111=Industrial Input/Output-   112=Mixed Gas Outlet-   113=CTP Calculator-   114=Third Flow Meter-   115=Third Gas (Inlet)-   116=Fourth Flow Meter-   117=Fourth Gas (Inlet)-   118=Signal from Third Flow Meter to CTP Calculator-   119=Signal from Fourth Flow Meter to CTP Calculator-   120=Mixture Composition Control-   121=Imbedded Controller (internal to Flow Meters 102, 105, 113, and    116)-   122=Control Valve (internal to Flow Meters 102, 105, 113, and 116)-   123=Manual Set Point Trim Control-   124=Pressure Sensor-   125=Pressure Sensor Signal to First Flow Meter-   126=Pressure Sensor Signal to Second Flow Meter-   127=Pressure Sensor Signal to Third Flow Meter-   128=Pressure Sensor Signal to Fourth Flow Meter-   129=First Flow Meter Gas Outlet-   130=Second Flow Meter Gas Outlet-   131=Third Flow Meter Gas Outlet-   132=Fourth Flow Meter Gas Outlet-   133=Signal from Manual Set Point Control to Mixture Composition    Control-   134=Signal from Mixture Composition Control to First Flow Meter-   135=Signal from Mixture Composition Control to Second Flow Meter-   136=Signal from Mixture Composition Control to Third Flow Meter-   137=Signal from Mixture Composition Control to Fourth Flow Meter-   200=Combined Gas Flow (instantaneous)-   300=Combined Gas Flow (cumulative)

DESCRIPTION OF PREFERRED EMBODIMENTS

Illustrative embodiments of the invention are described below. While theinvention is susceptible to various modifications and alternative forms,specific embodiments thereof have been shown by way of example in thedrawings and are herein described in detail. It should be understood,however, that the description herein of specific embodiments is notintended to limit the invention to the particular forms disclosed, buton the contrary, the intention is to cover all modifications,equivalents, and alternatives falling within the spirit and scope of theinvention as defined by the appended claims.

It will of course be appreciated that in the development of any suchactual embodiment, numerous implementation-specific decisions must bemade to achieve the developer's specific goals, such as compliance withsystem-related and business-related constraints, which will vary fromone implementation to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking for those of ordinary skill in theart having the benefit of this disclosure.

As used herein, the term “instantaneous” is defined as performing acalculation as quickly as the flow rate measurements and the embeddedcontroller permit, and with no calculation delay after the reception ofthe measurement.

As used herein, the term “cumulative” is defined as performing acalculation over predetermined, and extended, period of time, therebydetermining an overall average value.

As used herein, the term “first interval of time” is defined as aninterval of between about 1/60th of a second to about 1/10th of asecond. This is the time required for the “instantaneous” (as definedherein) measurements and calculations to be performed.

As used herein, the term “second interval of time” is defined as aninterval of between about 5 minutes and about 60 minutes. This is thetime over which the “instantaneous” measurements and calculations aresummed in order to calculate the “cumulative” (as defined herein)values. The “second interval of time may also be any duration for whichthe skilled artisan will find the results enlightening or useful

As used herein, the term “calculated theoretical percentage” (CTP) ofone component gas in a gas mixture is defined as ratio of the actual,measured flow rate of one of the component gases to the actual, measuredtotal flow of all component gases in the mixture. This CTP may then becompared to the input ratio to determine the accuracy and/or precisionof the mixer, and may be adjusted by the manual set point trim control.

As used herein, the term “instantaneous calculated theoreticalpercentage” of one component gas in a gas mixture is defined as theabove described CTP calculation, with the calculation being performed asquickly as the flow rate measurements and the embedded controller permit(the first predetermined intervals of time) and with no calculationdelay after the reception of the measurement.

As used herein, the term “cumulative calculated theoretical percentage”of one component gas in a gas mixture is defined as the above describedCTP calculation, with the calculation being performed over apredetermined, and extended, period of time (the second predeterminedinterval of time), thereby determining an overall average CTP.

As used herein, the term “mixture composition control” is defined as amechanism that allows an operator to input a desired gas mixturecomponent percent composition, and which adjusts associated flow controldevices, by means of feedback signals, to maintain the desiredcomposition as operational conditions (pressure, total flow rate, etc.)varies. This value will typically be displayed on a control panel.

It should be noted that the “mixture composition control” isfundamentally different, and functionally separate, from the “calculatedtheoretical percentage”. The “calculated theoretical percentage” usesfeedback to make a calculation, but does not actively adjust any of theflow rates. In contrast, the “mixture composition control” uses feedbackto actively adjust the flow rates as necessary to maintain the desiredflow rate. Specifically, the “mixture composition control” isunconcerned with the total flow rate the actual mixed gas, but is onlyconcerned with the flow rates of the individual flow meters. The“mixture composition control” modulates the flow rates of the individualflow meters in order to best achieve the input value.

As used herein, the term” composition trim input” is defined as amechanism that allows an operator to provide real-time adjustments to asystem that is operated by a mixture composition control, that willalter the output composition, without affecting the original desired gasmixture component percent composition input. This value will typicallybe displayed on a control panel.

Turning to FIGS. 1 and 3, a method of mixing two gases and determiningan instantaneous calculated theoretical percentage is presented. In oneembodiment of this invention, the method of mixing includes first flowmeter 103, second flow meter 105, and CTP calculator 113. A first gasstream 104 is provided to the inlet of first flow meter 103, whichmeasures the flow rate of first gas stream 104 at a first predeterminedinterval of time and sends a signal 101 to the CTP calculator 113. Asecond gas stream 106 is provided to the inlet of second flow meter 105,which measures the flow rate of second gas stream 106 at the firstpredetermined interval of time and sends a signal 102 to the CTPcalculator 113. The first predetermined interval of time may be between1/60 of a second and 1/10 of a second.

After passing through the flow meters, the first gas 129 is combinedwith the second gas 130, to form the combined gas stream 108. The firstmeasured gas flow 101 and the second measured gas flow 102 are addedtogether, thereby determining the total instantaneous gas flow 200 atthe predetermined intervals of time. The total gas flow may be less than8000 scfh. The measured first gas flow 101 is divided by the totalinstantaneous gas flow 200, thereby determining an instantaneouscalculated theoretical percentage CTP₁ for the first gas flow 101 at thefirst predetermined intervals of time.

The measured second gas flow 102 is divided by the total instantaneousgas flow 200, thereby determining an instantaneous calculatedtheoretical percentage CTP₂ for the second gas flow 102 at the firstpredetermined intervals of time. Either an alarm may be sounded, and/orthe first gas flow and the second gas flow may be terminated, if eitherthe instantaneous calculated theoretical percentage CTP₁ for the firstgas flow 101 or the instantaneous calculated theoretical percentage CTP₂for the second gas flow 102 exceeds a predetermined range value.

An embedded controller may be configured to measure the first gas flow101 and second gas flow 102, calculate the total instantaneous gas flow200, calculate the instantaneous theoretical percentage for the firstgas flow CTP₁ and second gas flow CTP₂, and sound the alarm if thepredetermined range value is exceeded. In this embodiment, noprogrammable logic controller is required. The embedded controller maybe monitored by a data logging system. The embedded controller mayinterface with an output, allowing the user to access real time CTPcalculations or historical CTP data. The embedded controller may includeat least one industrial input/output. The first gas flow 101, the secondgas flow 102, and/or the combined gas flow 200 may be used in foodprocessing, Modified Atmospheric Packaging, welding, inerting,blanketing, beverage production, etc.

Again, with reference to FIGS. 1 and 3, a method of mixing two gases anddetermining cumulative calculated theoretical percentage is presented.In one embodiment of this invention, the method of mixing includes firstflow meter 103, second flow meter 105, and CTP calculator 113. A firstgas stream 104 is provided to the inlet of first flow meter 103, whichmeasures the flow rate of first gas stream 104 at a first predeterminedinterval of time and sends a signal 101 to the CTP calculator 113. Themeasured first gas flow rate 101 is totaled over a second predeterminedperiod of time. A second gas stream 106 is provided to the inlet ofsecond flow meter 105, which measures the flow rate of second gas stream106 at the first predetermined interval of time and sends a signal 102to the CTP calculator 113. The measured second gas flow rate 102 is alsototaled over a second predetermined period of time.

After passing through the flow meters, the first gas 129 is combinedwith the second gas 130, to form the combined gas stream 108. The firstmeasured gas flow 101 and the second measured gas flow 102 are addedtogether, thereby determining the instantaneous total gas flow 200 atthe first predetermined intervals of time. The total first measured gasflow 101 and the total second measured gas flow 102 are added together,thereby determining the total cumulative gas flow 300 at the secondpredetermined interval of time. The total gas flow may be less than 8000scfh.

The measured first gas flow 101 is divided by the total instantaneousgas flow 200, thereby determining an instantaneous calculatedtheoretical percentage CTP₁ for the first gas flow 101 at the firstpredetermined intervals of time. The measured second gas flow 102 isdivided by the total instantaneous gas flow 200, thereby determining aninstantaneous calculated theoretical percentage CTP₂ for the second gasflow 102 at the first predetermined intervals.

The measured first gas flow 101 is divided by the total continuous gasflow 300, thereby determining a calculated continuous theoreticalpercentage CTP_(1C) for the first gas flow 101 at the secondpredetermined interval of time. The measured second gas flow 102 isdivided by the total continuous gas flow 300, thereby determining acalculated cumulative theoretical percentage CTP_(2C) for the second gasflow 102 at the second predetermined interval of time.

Either an alarm may be sounded, and/or the first gas flow and the secondgas flow may be terminated, if the instantaneous calculated theoreticalpercentage CTP for either the first gas flow 101 or the second gas flow102 exceeds a predetermined range value. Likewise, either an alarm maybe sounded and/or either gas flow may be terminated if the cumulativecalculated theoretical percentage CTP for either the first gas flow 101or the second gas flow 102 exceeds a predetermined range value.

An embedded controller may be configured to measure the first gas flow101 and second gas flow 102, calculate the total instantaneous gas flow200, calculate the total cumulative gas flow 300, calculate theinstantaneous theoretical percentage for the first gas flow CTP₁ andsecond gas flow CTP₂, calculate the cumulative theoretical percentagefor the first gas flow CTP_(1C) and second gas flow CTP_(2C), and soundthe alarm if the predetermined range value is exceeded. In thisembodiment, no programmable logic controller is required. The embeddedcontroller may be monitored by a data logging system. The embeddedcontroller may include at least one industrial input/output. The firstgas flow 101, the second gas flow 102, and/or the combined gas flow 200may be used in food processing, Modified Atmospheric Packaging, welding,inerting, blanketing, beverage production, etc.

The above described, non-limiting embodiments of the present inventiondescribe the mixing of two gases and the calculation of instantaneousCTP and cumulative CTP for each of the two streams. This method may beextended to N gas streams.

Turning now to FIGS. 2 and 4, a method of mixing N gases and determiningan instantaneous calculated theoretical percentage is presented. In oneembodiment of this invention, the method of mixing includes N flowmeters 103, 105, 114, 116, and CTP calculator 113. In the following, asystem with 4 flow meters is discussed, however there need not be aneven number of flow meters. The logic and method may be applied to anynumber of flow meters.

N gas streams 104, 106, 107, 115 are provided to the inlet of the N flowmeters 103, 105, 114, 116, which measures the flow rate of each of the Ngas streams at a first predetermined interval of time and sends a signal101, 102, 118, 119 to the CTP calculator 113.

After passing through the N flow meters 103, 105, 114, 116, the N gasstreams 104, 106, 107, 115 are combined to form the combined gas stream108. The N measured gas flows 101, 102, 118, 119 are added together,thereby determining the total instantaneous gas flow 200 at thepredetermined intervals of time. The total gas flow may be less than8000 scfh. The measured first gas flow of each stream 101, 102, 118, 119are divided by the total instantaneous gas flow 200, thereby determiningan instantaneous calculated theoretical percentage CTP_(N) for each gasstream at the first predetermined intervals of time.

Either an alarm may be sounded, and/or one or more of the N gas flowsmay be terminated, if either the instantaneous calculated theoreticalpercentage CTP_(N) for that gas flow 101 exceeds a predetermined rangevalue.

An embedded controller may be configured to measure the N gas flows,calculate the total instantaneous gas flow 200, calculate theinstantaneous theoretical percentage for each of the N gas flows, andsound the alarm if the predetermined range value is exceeded by any ofthe N gas flows. In this embodiment, no programmable logic controller isrequired. The embedded controller may be monitored by a data loggingsystem. The embedded controller may interface with an output, allowingthe user to access real time CTP calculations or historical CTP data.The embedded controller may include at least one industrialinput/output. One or more of the N gas flows and/or the combined gasflow 200 may be used in food processing, Modified Atmospheric Packaging,welding, inerting, blanketing, beverage production, etc.

Again, with reference to FIGS. 2 and 4, a method of mixing N gases anddetermining cumulative calculated theoretical percentage is presented.In one embodiment of this invention, the method of mixing includes Nflow meter 103, 105, 114, 116, and CTP calculator 113. In the following,a system with 4 flow meters is discussed, however there need not be aneven number of flow meters. The logic and method may be applied to anynumber of flow meters.

N gas streams 104, 106, 107, 115 are provided to the inlet of the N flowmeters 103, 105, 114, 116, which measures the flow rate of each of the Ngas streams at a first predetermined interval of time and sends a signal101, 102, 118, 119 to the CTP calculator 113. The measured flow rate foreach of the N gases is totaled over a second predetermined period oftime.

The N measured gas flows 101, 102, 118, 119 are added together, therebydetermining the total instantaneous gas flow 200 at the predeterminedintervals of time. The total measured gas flows for each of the N gasesare added together, thereby determining the total cumulative gas flow300 at the second predetermined interval of time for each of the N gasflows. The total gas flow may be less than 8000 scfh.

The measured first gas flow of each stream 101, 102, 118, 119 aredivided by the total instantaneous gas flow 200, thereby determining aninstantaneous calculated theoretical percentage CTP_(N) for each gasstream at the first predetermined intervals of time. The measured gasflow for each of the N streams is divided by the total continuous gasflow 300, thereby determining a calculated continuous theoreticalpercentage CTP_(NC) for the each of the gas flows at the secondpredetermined interval of time.

Either an alarm may be sounded, and/or one or more of the N gas flowsmay be terminated, if either the cumulative calculated theoreticalpercentage CTP_(N) for that gas flow exceeds a predetermined rangevalue.

An embedded controller may be configured to measure the N gas flows,calculate the total instantaneous gas flow 200, calculate theinstantaneous theoretical percentage for each of the N gas flows, andsound the alarm if the predetermined range value is exceeded by any ofthe N gas flows, calculate the cumulative theoretical percentage foreach of the N gas flows CTP_(NC), and sound the alarm if thepredetermined range value is exceeded. In this embodiment, noprogrammable logic controller is required. The embedded controller maybe monitored by a data logging system. The embedded controller mayinclude at least one industrial input/output. One or more of the N gasflows and/or the combined gas flow 200 may be used in food processing,Modified Atmospheric Packaging, welding, inerting, blanketing, beverageproduction, etc.

Turning back to FIGS. 1 and 3, a method of mixing two gases and flowmatching is presented. In one embodiment of this invention, the methodincludes a first gas flow meter 103, a second gas flow meter 105, apressure sensor 124, and a mixture composition control 120, which allowsa mixed gas flow to be formed at a predetermined composition C₁.

A first gas flow 104 enters the first gas flow meter 103, and a firstdesired gas flow rate F₁ is determined by the mixture compositioncontrol 120. A second gas flow 106 enters the second gas flow meter 105,and a second desired gas flow rate F₂ is determined by the mixturecomposition control 120. The first gas 129 and the second gas 130 aremixed, thereby producing a mixed gas flow 108 at the predeterminedcomposition C₁ and at a line pressure P_(L), with a total gas flowF_(T). The total gas flow F_(T) may be less than 8000 scfh.

The pressure sensor 124 provides a pressure signal 125 to the mixturecomposition control 120, which adjusts the flow commands to the flowmeters as necessary to maintain a predetermined line pressure P_(L).Simultaneously, the mixture composition control 120 provides a signal134 to the first gas flow meter and a signal 135 the second gas flowmeter, allowing the flow meters to adjust as necessary to maintain thepredetermined composition C₁.

The above described, non-limiting embodiments of the present inventiondescribe the mixing of two gases and the and the means of flow matchingthe two streams. This method may be extended to N gas streams.

Turning back to FIGS. 2 and 4, a method of mixing N gases and flowmatching is presented. Where N is 3 or more. In one embodiment of thisinvention, the method includes N gas flow meters 103, 105, 114, 116, apressure sensor 124, and a mixture composition control 120, which allowsa mixed gas flow to be formed at a predetermined composition C₁. In thefollowing, a system with 4 flow meters is discussed, however there neednot be an even number of flow meters. The logic and method may beapplied to any number of flow meters.

Each gas flow 104, 106, 107, 115 enters an associated gas flow meter103, 105, 114, 116, and a desired gas flow rate F_(N) is determined bythe mixture composition control 120. The N gas streams 129, 130, 131,132 are mixed, thereby producing a mixed gas flow 108 at thepredetermined composition C₁ and at a line pressure P_(L), with a totalgas flow F_(T). The total gas flow F_(T) may be less than 8000 scfh.

The pressure sensor 124 provides a pressure signal 125 to the mixturecomposition control 120, which adjusts the flow commands to the flowmeters as necessary to maintain a predetermined line pressure P_(L).Simultaneously, the mixture composition control 120 provides a signal134, 135, 136, 137 to each of the first gas flow meters, allowing theflow meters to adjust as necessary to maintain the predeterminedcomposition C₁.

Turning back to FIGS. 1 and 3, a method of mixing two gases with acontrol trim feature is presented. In one embodiment of this invention,the method includes a first gas flow meter 103, a second gas flow meter105, and a mixture composition control 120. The mixture compositioncontrol 120 comprises a predetermined composition input control and acomposition trim input (manual set point trim control) 123, which allowsa mixed gas flow to be formed at a predetermined composition C₁ withfine tuning (trim) adjustments as needed.

A first gas flow 104 enters the first gas flow meter 103, and a firstdesired gas flow rate F₁ is determined by the mixture compositioncontrol 120. A second gas flow 106 enters the second gas flow meter 105,and a second desired gas flow rate F₂ is determined by the mixturecomposition control 120. The first gas 129 and the second gas 130 aremixed, thereby producing a mixed gas flow 108 at the predeterminedcomposition C₁. The composition trim input may be used to vary theactual composition of the mixed gas, without modifying the predeterminedcomposition input.

The above described, non-limiting embodiments of the present inventiondescribe the mixing of two gases and the and the means of flow matchingthe two streams. This method may be extended to N gas streams.

Turning back to FIGS. 2 and 4, a method of mixing N gases and flowmatching is presented. Where N is 3 or more. In one embodiment of thisinvention, the method includes N gas flow meters 103, 105, 114, 116, anda mixture composition control 120. The mixture composition control 120comprises a predetermined composition input control and a compositiontrim input (manual set point trim control) 123, which allows a mixed gasflow to be formed at a predetermined composition C₁ with fine tuning(trim) adjustments as needed.

Each gas flow 104, 106, 107, 115 enters an associated gas flow meter103, 105, 114, 116, and a desired gas flow rate F_(N) is determined bythe mixture composition control 120. The N gas streams 129, 130, 131,132 are mixed, thereby producing a mixed gas flow 108 at thepredetermined composition C₁, with a total gas flow F_(T). The total gasflow F_(T) may be less than 8000 scfh. The composition trim input may beused to vary the actual composition of the mixed gas, without modifyingthe predetermined composition input.

It will be understood that many additional changes in the details,materials, steps and arrangement of parts, which have been hereindescribed in order to explain the nature of the invention, may be madeby those skilled in the art within the principle and scope of theinvention as expressed in the appended claims. Thus, the presentinvention is not intended to be limited to the specific embodiments inthe examples given above.

What is claimed is:
 1. A method of mixing between 2 and 4 gases,comprising: providing a mixture composition control, comprising apredetermined composition input and a composition trim input, providingN gas flow meters, comprising a N gas streams, and N desired gas flowrates determined by the mixture composition control, wherein N isbetween 2 and 4, mixing the N gas streams, thereby producing a mixed gasstream at the predetermined composition and at a line pressure,adjusting the N flow meters to adjust the N gas streams to maintain theline pressure at a predetermined value, while maintaining thepredetermined composition, adjusting the composition trim input to varythe composition of the mixed gas stream, without modifying thepredetermined composition input.
 2. The method of claim 1, wherein oneor more of the N gas streams, and/or the mixed gas outlet comprises agas used in food processing, Modified Atmospheric Packaging, welding,industrial inerting, blanketing, or beverage production.